Telemann was born in Magdeburg, the capital of the Duchy of Magdeburg, Brandenburg - Prussia, into an upper middle class family. His parents were Heinrich Telemann, deacon at the Church of the Holy Spirit (Helig-Geist-Kirche) in Magdeburg, and Maria Haltmeier, daughter of a clergyman from Regensburg. Many of the family members worked for the church and only a few distant relatives were musicians. The composer himself claimed that he inherited the talent for music from his mother, whose nephew Joachim Friedrich was Kantor at Verden (Telemann would later publish a treatise by Joachim Friedrich's son, who became an organist). On his father's side, only a single relative is known to have been a professional musician: Heinrich Thering, Telemann's great-grandfather, served as Kantor at Halberstadt in the late 16th century. Telemann's brother Heinrich Matthias (1672 – 1746) eventually became a clergyman.

Telemann's father died in 1685, leaving Maria to raise the children and oversee their education. Telemann studied at the Altstädtisches Gymnasium and at the Domschule, where he was taught the catechism, Latin and Greek. At age 10 he took singing lessons and studied keyboard playing for two weeks with a local organist. This was enough to inspire the boy to teach himself other instruments (recorder, violin and zither) and start composing. His first pieces were arias, motets, and instrumental works, and at age 12 he composed his first opera, Sigismundus. Neither Maria nor her advisers were supportive of these endeavours, however. They confiscated all of the boy's instruments and forbade him any musical activities, yet Telemann continued composing, in secret. In late 1693 or early 1694 his mother sent him to a school in Zellerfeld, hoping that this would convince her son to choose a different career. However, the superintendent of the school, Caspar Calvoer, recognized Telemann's talents and even introduced him to musical theory; Telemann continued composing and playing various instruments, taught himself thoroughbass and regularly supplied music for the church choir and the town musicians.

In 1697 Telemann left for Hildesheim, where he entered the famous Gymnasium Andreanum. Here too his talents were recognized and in demand: the rector himself commissioned music from Telemann. The young composer frequently travelled to courts at Hanover and Brunswick where he could hear and study the latest musical styles. Composers such as Antonio Caldara, Arcangelo Corelli, and Johann Rosenmuller were early influences. Telemann also continued studying various instruments, and eventually became an accomplished multi-instrumentalist: at Hildesheim he taught himself flute, oboe, chalumeau, viola da gamba, double bass, and bass trombone. After graduating from Gymnasium Andreanum (with excellent results, despite his musical activities), Telemann went to Leipzig in late 1701 to become a student at the Leipzig University, where he intended to study law. In his 1718 autobiography Telemann explained that this decision was taken because of his mother's urging. However, some 22 years later, in the 1740 autobiography, he offered a different explanation, claiming that he was motivated by his desire for university education. This was not to come: according to Telemann himself, a setting of Psalm 6 by him inexplicably found its way into his luggage and was found by his roommate at the university. The work was subsequently performed and so impressed those who heard it that the mayor of Leipzig himself approached Telemann and commissioned him to regularly compose works for the city's two main churches (Thomaskirche and Nikolaikirche).

Once he established himself as a professional musician in Leipzig, Telemann became increasingly active in organizing the city's musical life. From the start, he relied heavily on employing students: the very first ensemble he founded was a student collegium musicum that had some 40 members. They gave public concerts and also provided music for the Neukirche. In 1702 Telemann became director of the opera house Opernhaus auf dem Brühl, where too he employed student performers. Finally, when Telemann got the post of organist and music director at the Neukirche, he only played the organ once, and assigned the organist's duties to his students. Between 1702 and 1705 Telemann composed at least eight operas, four of which went to the Leipzig opera house and four to the Weissenfels court. During his time at Leipzig, he was continually influenced by the music of Handel, whom he met earlier, in 1701. He also studied the works of Johann Kuhnau, Kantor of the Thomaskirche and city director of music in Leipzig; in his later years, Telemann recounted how much he learned about counterpoint from Kuhnau's work.

However, Telemann's growing prominence and methods caused a conflict between him and Kuhnau. By employing students Telemann took away a major resource for Kuhnau's choir (and church music in Leipzig in general); Kuhnau was also concerned that students were too frequently performing in operas, leaving them with less time to devote to church music. Denouncing Telemann as an "opera musician", Kuhnau petitioned the city council several times against the younger composer. In the end, however, his efforts proved fruitless, and the only thing the council did was to forbid Telemann to appear on the operatic stage. Kuhnau's rights were never fully restored, not even after Telemann left Leipzig.

In 1704 Telemann received an invitation to become Kapellmeister for the court of Count Erdmann II of Promnitz at Sorau (now Żary, in Poland). Leipzig authorities only granted him resignation in early 1705, however, and he arrived in Sorau in June. This new position allowed him to study contemporary French music, which was particularly popular at the court: the works of Lully and Campra. Also, when the court spent six months in Pleß (now Pszczyna), Telemann had an opportunity to hear and study Polish and Moravian folk music, which fascinated and inspired him. In performing his duties at the court, Telemann was as prolific as in Leipzig, composing at least 200 ouvertures, by his own recollection, and other works. Unfortunately, the Great Northern War put an end to Telemann's career at Sorau. In late January or early February 1706 he was forced to flee from the invading troops of the Swedish King Charles XII. He spent some time in Frankfurt an der Oder before returning to Sorau in the summer.

The details of how Telemann obtained his next position are unknown. Around 1707 – 1708 he entered the service of Duke Johann Wilhelm of Saxe - Eisenach, becoming Konzertmeister on 24 December 1708 and Secretary and Kapellmeister in August 1709. Thus began one of the most productive periods in Telemann's life: during his tenure at Eisenach he composed a wealth of instrumental music (sonatas and concertos), and numerous sacred works, which included four or five complete annual cycles of church cantatas, 50 German and Italian cantatas, and some 20 serenatas. In 1709 he made a short trip to Sorau to marry Amalie Louise Juliane Eberlin, lady-in-waiting to the Countess of Promnitz and daughter of the musician Daniel Eberlin. They went back to Eisenach, where in January 1711 Amalie Louise gave birth to a daughter. Unfortunately, the mother died soon afterwards; Telemann's marriage lasted only for 15 months. The event had a profound effect on the composer: he later recounted experiencing a religious awakening, and also published "Poetic Thoughts" on the death of his first wife in 1711. By the end of that year he was frustrated with court life and started seeking another appointment. He declined an offer from the Dresden court, since he wanted to work with greater artistic freedom; Telemann wanted a post similar to the one he had in Leipzig. Sometime between late December 1711 and early January 1712 he applied for the newly vacant Frankfurt post of city director of music and Kapellmeister at the Barfüsserkirche. The application was successful and Telemann arrived to Frankfurt on 18 March 1712.

Telemann's new duties were similar to those he had in Leipzig. He provided various music for two churches, Barfüsserkirche and Katharinenkirche (composing, among other pieces, more annual cycles of cantatas), as well as for civic ceremonies; he also revived the city's collegium musicum. After May 1712 Telemann also served as administrator and treasurer of the Haus Braunfels, administrator of a charitable foundation, and organizer of a tobacco collegium. On 28 August 1714 he married his second wife, Maria Catharina Textor, daughter of a council clerk. The couple had nine children (none became musicians), but the marriage would later prove disastrous for Telemann. The following year he began publishing his music; four collections of instrumental pieces appeared within the next three years, and many more publications would follow. On 11 March 1717 Telemann was appointed Kapellmeister von Haus aus at Eisenach: he fulfilled the duties of the position by regularly sending new music from Frankfurt to Eisenach.

On 10 July 1721 Telemann was invited to work in Hamburg as Kantor of the Johanneum Lateinschule and musical director of the city's five largest churches, succeeding Joachim Gerstenbüttel. The composer accepted; he remained in Hamburg for the rest of his life. The years spent in the city were the most productive period of his life. Once again he was required to compose numerous cantatas, not only for the churches but also for civic ceremonies; he also gave public concerts, led another collegium musicum, and assumed the directorship of the opera house Gänsemarktoper. Initially, however, Telemann encountered a number of problems: some church officials found opera and collegium musicum performances to be objectionable (for "inciting lasciviousness"), and the city printer was displeased with Telemann publishing printed texts for his yearly Passions. The former matter was resolved quickly, but Telemann's exclusive right to publish his own work was only recognized in full in 1757. Telemann's opera productions were not particularly popular, and eventually the opera house had to be closed down in 1738.

It is probably these difficulties that prompted Telemann to apply, already in 1722, for the post of Thomaskantor in Leipzig (Kuhnau died on 5 June that year). Of the six musicians who applied, he was the favored candidate, even winning the approval of the city's council. Telemann declined the position, but only after using the offer as leverage to secure a pay raise for his position in Hamburg. When Telemann declined the job, it was offered to Christoph Graupner, who also declined it — though chiefly because he could not secure a dismissal from his employer the Landgrave of Hesse - Darmstadt. This paved the way for J.S. Bach, who went to occupy the position for the rest of his life. Telemann returned to Hamburg, but would still supplement his income by taking up additional jobs: in 1723 – 1726 he served as Kapellmeister von Haus aus to the Bayreuth court, and between 1725 and 1730 he acted as corresponding agent to the court at Eisenach, supplying news from northern Europe.

In Hamburg Telemann started publishing his literary works: poems, texts for vocal music, sonnets, poems on the deaths of friends and colleagues. From 1725 he actively published his music as well, engraving and advertising the editions himself. More than 40 volumes of music appeared between 1725 and 1740 and these were widely distributed across Europe, owning to Telemann's numerous contacts in various countries. All this publishing activity, however, was in part driven by the need for money. Telemann's wife Maria Catherina amassed a very large gambling debt, 4400 Reichsthaler, which amounted to more than Telemann's annual income. The marriage has been troubled already by early 1720s, as Maria Catherina was publicly rumored to be having an affair with a Swedish military officer. Telemann's friends in Hamburg organized a collection to save the composer's finances, and eventually he was saved from bankruptcy; by 1736 Maria had left Telemann's home. She outlived her husband by some eight years and died in 1775 at a convent in Frankfurt.

In late September or early October 1737 Telemann took an extended leave from Hamburg and went to Paris. There he countered various unauthorized publications of his music by obtaining his own publishing privilege. He immediately published several works, most importantly the Nouveaux quatuors which were enthusiastically received by the court and the city musicians. Telemann returned to Hamburg by the end of May 1738. Around 1740 his musical output fell sharply, even though he continued fulfilling his duties as Hamburg music director. He became more interested in music theory and completed a treatise on the subject, Neues musicalisches System (1742/3, published 1752). He also took up gardening and cultivating rare plants, a popular Hamburg hobby which was shared by Handel. Telemann still followed European musical life, however: throughout the 1740s and the 1750s he exchanged letters and compositions with younger composers such as C.P.E. Bach, Franz Benda, Johann Friedrich Agricola, and others.

After Telemann's eldest son Andreas died in 1755, he assumed the responsibility of raising Andreas' son Georg Michael Telemann, who eventually became a composer. In his later years, Telemann's eyesight began to deteriorate, and he was increasingly troubled by health problems. This led to a further decline in his output around 1762, however, he was still capable of composing music of highest quality, and continued to write until his death on the evening of 25 June 1767. The cause of death was a "chest ailment"; he was buried on 29 June in the Johannisfriedhof. He was succeeded at his Hamburg post by Carl Philipp Emmanuel Bach.

Telemann was the most prolific composer of his time: his oeuvre comprises more than 3000 pieces. The first accurate estimate of the number of his works were provided by musicologists only during the 1980s and the 1990s, when extensive thematic catalogues were published. During his lifetime and the latter half of the 18th century Telemann was very highly regarded by colleagues and critics alike. Numerous theorists (Marpurg, Mattheson, Quantz, and Scheibe, among others) cited his works as models, and major composers such as J.S. Bach and Handel bought and studied his published works. He was immensely popular not only in Germany but in the rest of Europe as well: orders for editions of Telemann's music came from France, Italy, Holland, Belgium, Scandinavian countries, Switzerland, and Spain. It was only in early 19th century that his popularity came to a sudden halt. Most lexicographers started dismissing him as a "polygraph" who composed too many works, a Vielschreiber for whom quantity came before quality. Such views were influenced by an account of Telemann's music by Christoph Daniel Ebeling, a late 18th century critic who in fact praised Telemann's music and only made passing critical remarks of his productivity. After the Bach revival, Telemann's works were judged as inferior to Bach's and lacking in religious fervour. Particularly striking examples of such unfair judgements were produced by noted Bach biographers Philipp Spitta and Albert Schweitzer, who criticized Telemann's cantatas and then praised works they thought were composed by Bach — but which were, in fact, composed by Telemann, as was shown by later research. The last performance of a substantial work by Telemann (Der Tod Jesu) occurred in 1832, and it was not until the 20th century that his music started being performed again. The revival of interest in Telemann began in the first decades of the 20th century and culminated in the Bärenreiter critical edition of the 1950s. Today each of Telemann's works is usually given a TWV number. TWV stands for Telemann - Werke - Verzeichnis (Telemann Work Catalogue).

Telemann's music was one of the driving forces behind the late Baroque and the early Classical styles. Starting in the 1710s he became one of the creators and the foremost exponents of the so-called German mixed style, an amalgam of German, French, Italian and Polish styles. Over the years, his music gradually changed and started incorporating more and more elements of the galant style, but he never completely adopted the ideals of the nascent Classical era: Telemann's style remained contrapuntally and harmonically complex, and already in 1751 he dismissed much contemporary music as too simplistic. Composers he influenced musically included pupils of J.S. Bach in Leipzig, such as Wilhelm Friedmann Bach, Carl Philipp Emmanuel Bach and Johann Friedrich Agricola, as well as those composers who performed under his direction in Leipzig (Christoph Graupner, Johann David Heinichen and Johann Georg Pisendel), composers of the Berlin lieder school, and finally, his numerous pupils, none of whom, however, became major composers.

Equally important for the history of music were Telemann's publishing activities. By pursuing exclusive publication rights for his own works, he set one of the most important early precedents for regarding music as the intellectual property of the composer. The same attitude informed his public concerts, where Telemann would frequently perform music originally composed for ceremonies attended only by a select few members of the upper class.